General purpose or crystal polystyrene is used in a number of applications, including household and rigid packaging, where clarity or translucency is required. While general purpose polystyrene is suitable for such applications, it has a fairly low toughness. That is, it has low impact resistance. This drawback can be overcome by incorporating rubber into the polystyrene but it results in a loss of clarity or increasing haze.
U.S. Pat. No. 5,079,296, issued Jan. 7, 1992 to the assignee herein, discloses clear tough alloys. However, to obtain the combination of clarity and toughness, it is necessary to use a three component system, namely:
(i) a brittle polymer which is a clear thermoplastic; PA1 (ii) a block copolymer (typically K resin .RTM.); and PA1 (iii) an impact modified polymer (e.g. HIPS). PA1 (i) from 95 to 99.5, preferably from 99 to 97, weight % of a copolymer comprising: PA1 (ii) from 5 to 0.5, preferably from 3 to 1, weight % of an impact modified polymer comprising: PA1 to which has been grafted at least a portion of:
The K resin .RTM. is a relatively expensive component in the above blend. Applicants have discovered a blend having high clarity and good toughness while eliminating an essential component of the 296 patent.
There is a need for a relatively tough, clear polymer blend.